1. Field of the Invention
The present invention relates to a cooling device of an electronic part arranged in a PC server or a UNIX server, for example. The present invention also relates to an electronic apparatus including such a cooling device.
2. Description of the Related Art
In a PC server and a UNIX server playing the central role in the network that has seen a rapid development in recent years, a plurality of substrate units are mounted, each including one or a plurality of integrated circuit elements or packages, typically represented by a processor generating much heat.
Performance of the processor has recently been improved and the number of semiconductor circuits mountable in one chip has increased sharply, resulting in a correspondingly increased heat generated by the processor. Once the temperature of the processor exceeds an operation guaranteed temperature (generally, 80xc2x0 C. to 100xc2x0 C.), however, the normal function of the processor may be adversely affected.
In order to solve this problem, Japanese Unexamined Patent Publication (Kokai) No. 6-334374, for example, discloses a cooling structure in which a heat conductive member is mounted on the back of a high heat generating chip such as a processor, and the heat conductive member is inserted in a heat sink base plate having a multiplicity of radiation fins thereby to form a heat transmission path, thereby making it possible to efficiently radiate the heat generated by the high heat generating chip.
The PC server and the UNIX server described above are often used in a stack of multiple layers in a rack or the like. In order to install a multiplicity of servers in a small space, each server is desirably as thin as possible. Nevertheless, the prior art described above poses the problem that the server cannot be made thin for the reason described below.
An object of the cooling structure described in Japanese Unexamined Patent Publication (Kokai) No. 6-334374 is to prevent the heat generated by a high heat generating chip from being transferred to the other chips. In order to achieve this object, the heat sink base plate is installed in considerably spaced relation with the chips, and the heat conductive member for coupling the high heat generating chip and the heat sink base plate is bent substantially in the shape of Z as viewed sideways. Due to this structure, a large space is formed between the heat conductive member and a chip arranged downstream of the high output heat generating chip in the cooling air (hereinafter referred to as the low output heat generating chip), with the result that the heat conduction to the low output heat generating chip is suppressed.
An attempt to reduce the thickness of the server having the conventional structure described above would make it necessary to reduce the intervals between the multilayered substrates which in turn leads to a correspondingly smaller interval between the heat sink base plate and the substrates. This smaller interval reduces the space for preventing the heat conduction in the neighborhood of the low output heat generating chip, thereby making it impossible to achieve the object of the conventional structure described above, i.e. the prevention of heat conduction to the low output heat generation chip. Also, a smaller interval between the heat sink base plate and the substrates further causes the heat conductive member arranged upstream of the low heat generating chip in the cooling air to further block a smooth flow of the cooling air, with the probable result that some areas are exposed to the cooling air more than other areas. Since the processor is expected to be improved in performance more and more in the future, with an increased heating value, it is considered difficult to form a thinner server with the conventional structure described above.
On the other hand, various components are mounted on the substrate and therefore both the heating value and the size are not uniform. In the area in the neighborhood of the processor constituting a high heat generating element, for example, the heat generation density is locally increased, while the heat generation density is comparatively small in the area where a integrated circuit element or a package constituting a low heat generating element is mounted. An attempt to reduce the temperature of the area having a large heat generation density below the operation guaranteed temperature by increasing the amount of the cooling air, for example, would excessively reduce the temperature of the area having a small heat generation density, with the result that the areas not required to be cooled are undesirably cooled. Especially in the case where the rotational speed of the cooling fan is limited for noise suppression, the uneven distribution of the heat generation density can be a stumbling block to a thickness reduction of the server.
In view of the aforementioned problem of the prior art, the object of the present invention is to provide a cooling device for an electronic part in which uneven distribution of the heat generation density is eliminated for an improved cooling efficiency of the electronic part.
In order to achieve this object, according to the present invention, there is provided a cooling device of an electronic part having a substrate, a first heat generating element mounted on the substrate, and a second heat generating element mounted on the substrate and generating less heat than the first heat generating element, the height of the first heat generating element when mounted on the substrate being greater than a height of the second heat generating element when mounted on the substrate, the cooling device comprising a heat conductive member to which heat is transmitted from the first heat generating element and radiation members mounted on said heat conductive member in heat transferring fashion, said radiation members extending toward the second heat generating element, the radiation members being also formed in a space between the combination of the first heat generating element and the heat conductive member and the second heat generating element.
An electronic apparatus according to the present invention comprises a plurality of package units including at least one substrate unit, which includes the feature.
In this cooling device, in the case where the elements are arranged in a limited space, the cooling efficiency of the first heat generating element can be improved by reducing the difference of the heat generation density between the neighborhood of the first heat generating element and the neighborhood of the second heat generating element through the heat conductive member and the radiation members.
Preferably, the heat transferring efficiency can be improved by appropriately making the heat conductive member from a plate formed of a material having an isotropic heat conduction and/or a material having both a high heat conductivity and an anisotropic heat conduction. By the way, the material having the isotropic heat conduction is a metal such as copper and aluminum and the material having the anisotropic heat conduction is carbon graphite or the like, but the invention is not limited to these materials.
The plate can transmit the heat more efficiently through heat pipes if one or a plurality of heat pipes are built therein.
Further, if the plate has a first heat pipe and a second heat pipe built therein in such a manner that the first heat pipe extends in a first direction and the second heat pipe extends in a second direction different from the first direction along the plane of the plate with heat pipes of one of the heat pipes bent to avoid interference with heat pipes of the other heat pipe at each intersection thereof, then the heat transmission in two directions of the plate can be improved further and the two heat pipes can be built into the plate in a compact form thereby making it possible to reduce the thickness of the plate, for example.
Also, if the plate extends in parallel to said substrate and has a notch and/or a hole for avoiding the parts mounted on the board, the plate can be extended more widely regardless of the size of the parts mounted on the substrate.
Further, if the plate has a plurality of portions having different spaced relations with the substrate, the plate can be bent to avoid tall parts such as a small substrate module arranged in a position perpendicular to the board. By doing so, the plate can be extended more widely regardless of the size of the parts mounted on the substrate.
Furthermore, if the portions of the plate described above are coupled to each other by heat pipes, different plate portions can be arranged in the neighborhood of tall parts and short parts, respectively, and coupled by heat pipes. In this way, the plate can be arranged in a wider range regardless of the size of the parts mounted on the board. Even in the case where the heat pipes are arranged in a direction crossing the flow of the cooling air, the cooling air flow is only slightly blocked as long as the heat pipes have a circular section.
In the electronic apparatus, in the case where the elements are arranged within a limited space, the cooling efficiency of the first heat generating element can be improved by reducing the difference in heat generation density between the neighborhood of the first heat generating element and the neighborhood of the second heat generating element through the heat conductive member and the radiation members. Thus, the thickness of each package unit can be reduced, so that a greater number of package units can be stacked without increasing the total height of the electronic apparatus.